(CNN) -- Colleen Whiteaker's three eldest daughters looked at her with concern.

They were beautiful, she thought, with their slim, athletic builds and porcelain skin. She hadn't wanted them to deal with the pain of being overweight, so she had taught them to eat nutritious foods and stay active.

Now they were throwing those lessons back in her face.

Miriam, Candace and Chloe tried to pitch their "intervention" like a fun plan. They bought their mom a gym membership and some new workout clothes. They tried to avoid talking about her weight problem directly, but eventually the truth came out.

"It was terrible," Candace remembers. "It's never something you want to bring up, especially to your mom. But really it was just hurting us to see her like that. We didn't want to have to worry about her dying."

Their mother was 5 feet 2 inches tall and weighed more than 200 pounds. She had become isolated and never wanted to participate in family get-togethers. The older girls were worried their youngest sister Celeste, 5 at the time, wouldn't get to know the wonderful, energetic mom with whom they had grown up.

"They were crying. I was crying," Colleen says. "It really hurt my feelings. ... I was like, 'I know I'm heavy. I know that, but I'm not unhealthy. I'm just supposed to be that weight.'

"They were like, 'Mom, I don't think that's true.' "

'I was trying to lose weight'

Colleen isn't sure how she put on so much weight. She was chubby as a child, and her weight fluctuated throughout adulthood. She didn't eat a lot of bad foods, staying away from fast food and fried fare. But she rarely exercised and says she has a slow metabolism.

Shortly after Celeste's birth, Colleen and her husband divorced. Stress, combined with an unusual work schedule and a new baby, kept the pounds on despite multiple attempts at dieting.

"It was discouraging because I wasn't just pretending like I didn't know I needed to lose weight," she says. "I was trying to lose weight. I wanted something to change."

Unfortunately, her daughters' intervention didn't work. It wasn't until Chloe and Candace's college graduation nearly six years later that she really took a good look in the mirror.

She was thrilled for her daughters and proud to be their mother, but she wasn't proud of the way she looked. She weighed close to 230 pounds. She dreaded meeting their college friends and taking a million photos.

On the way home -- embarrassed and miserable -- Colleen thought about what she could do. A few years earlier, her new husband had bought a Bowflex TreadClimber. It was sitting in their North Carolina house, practically unused. She promised herself she would start walking on it three times a week, for 20 minutes.

And that's what she did.

At the end of September 2011, she met her daughters at Kings Dominion, an amusement park in Virginia, for an annual trip. The girls noticed she had lost a bit of weight and complimented her.

"I was excited, but I didn't really want to ... make a huge deal of it because I didn't want her to feel like we were adding pressure," Candace says.

The girls' comments encouraged Colleen. She added another day to her routine, then another. Soon she was walking for 45 minutes, six days a week. The more she exercised, the more she was conscious of what she was eating. She started writing down her meals in a journal to get an idea of how much she was consuming each day.

Her goal was to go from a size 20 to a size 12. By May 2012, she was a size 2/4.

She had lost more than 110 pounds in about 10 months.

"She was ready to take on the world," Candace says. "She wanted to go out and do all these things. ... It was like having our old mom back."

Raiding daughters' closets fun

When she was overweight, Colleen says she never felt bad physically. "I did whatever I wanted to do, but I didn't want to do that much," she says with a laugh.

Today she says she feels "100% better."

"She has more energy than we do now," Candace says. "She's just very inspiring, and she just keeps going, and I love her for that."

Colleen was laid off before she jumped on the TreadClimber. She went on multiple job interviews that amounted to nothing. But her first interview after losing the weight resulted in a job offer.

She's not sure if it was her new body or her newfound confidence, but she knows people treat her differently now that she's slim.

"They see you as maybe having something to offer," she says.

Perhaps her favorite part of losing weight is borrowing her daughters' clothes. Before, she hated to go shopping to buy new clothes. Now when she visits, she doesn't even bother to pack -- instead preferring to raid their closets.

Celeste just turned 13, and Candace is happy her youngest sister will get to experience Colleen as the mom she remembers.

"She's very free-spirited and encouraging and happy," Candace says of her mother. "And that was being covered up by all that extra weight she was carrying around."

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